The present invention is directed to bicycles and, more particularly, to a method and apparatus for controlling a bicycle transmission.
A typical bicycle transmission may include a plurality of front sprockets that rotate with the pedal cranks, a plurality of rear sprockets that rotate with the rear wheel, and a chain that engages one of the front sprockets and one of the rear sprockets. A front derailleur may be mounted to the bicycle frame for shifting the chain among the plurality of front sprockets, and a rear derailleur may be mounted to the bicycle frame for shifting the chain among the plurality of rear sprockets. Manually operated switches or levers may control the front and rear derailleurs. More sophisticated systems use small electric motors to control the bicycle transmission. The motors may be controlled manually by the foregoing switches or levers, or automatically based on bicycle speed and/or cadence.
When shifting the chain from a first sprocket to a second sprocket, it is known that the position of the rear derailleur relative to the second sprocket needed to catch the chain on the second sprocket varies depending on the design of the derailleur, the design of the chain, the design of the sprockets, and even how fast the derailleur moves. Some derailleur transmissions shift xe2x80x9cearlyxe2x80x9d in that the chain catches the second sprocket before the derailleur is aligned with the second sprocket, while other derailleurs shift xe2x80x9clatexe2x80x9d in that the derailleur must be moved beyond the second sprocket before the chain catches the second sprocket. In either case, the derailleur usually is aligned with the second sprocket after the chain catches the second sprocket. Correctly moving the derailleur to accommodate these requirements is a challenge when designing motor-controlled transmissions.
The present invention is directed to a method and apparatus for controlling the operation of a bicycle transmission, and particularly a derailleur transmission. In one embodiment of the present invention, an apparatus for moving an electrically controlled bicycle derailleur from a first sprocket to a second sprocket comprises a derailleur position input for receiving a signal indicating a position of the derailleur; a memory storing a first reference derailleur position for the second sprocket; and a motion control circuit that provides a plurality of signals to move the derailleur from the first sprocket to the second sprocket. The plurality of signals comprises a first signal generated when the derailleur initially moves away from the first sprocket and a second signal generated when the derailleur is in close proximity to the second sprocket. If desired, the first signal may comprise a drive signal, and the second signal may comprise a deceleration signal.
In a more specific embodiment, the plurality of signals may further comprise a third signal to position the derailleur at the first reference derailleur position, wherein the first reference derailleur position may be a position aligned with the second sprocket. The memory may store a second reference derailleur position and a third reference derailleur position, wherein the motion control circuit generates the second and third signals when the derailleur is at the second and third reference derailleur positions, respectively. In some embodiments the second reference derailleur position may correspond to a position wherein the derailleur is aligned with the second sprocket, whereas in other embodiments the second reference derailleur position may correspond to a position wherein the derailleur is spaced apart from the second sprocket. The third reference position is usually, but not necessarily, spaced apart from the second sprocket, either between the first and second sprockets or outside the range between the first and second sprockets. The memory may be a volatile or nonvolatile memory, and the reference derailleur positions may be predetermined or calculated in real time.